linux-kernel - [PATCH 3.2 099/102] ext2: Fix fs corruption in ext2_get_xip

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Message-ID: <lsq.1414880883.645068768@decadent.org.uk>
Date:	Sat, 01 Nov 2014 22:28:03 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.2 099/102] ext2: Fix fs corruption in ext2_get_xip_mem()

3.2.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit 7ba3ec5749ddb61f79f7be17b5fd7720eebc52de upstream.

Commit 8e3dffc651cb "Ext2: mark inode dirty after the function
dquot_free_block_nodirty is called" unveiled a bug in __ext2_get_block()
called from ext2_get_xip_mem(). That function called ext2_get_block()
mistakenly asking it to map 0 blocks while 1 was intended. Before the
above mentioned commit things worked out fine by luck but after that commit
we started returning that we allocated 0 blocks while we in fact
allocated 1 block and thus allocation was looping until all blocks in
the filesystem were exhausted.

Fix the problem by properly asking for one block and also add assertion
in ext2_get_blocks() to catch similar problems.

Reported-and-tested-by: Andiry Xu <andiry.xu@...il.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext2/inode.c | 2 ++
 fs/ext2/xip.c   | 1 +
 2 files changed, 3 insertions(+)

--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -619,6 +619,8 @@ static int ext2_get_blocks(struct inode
 	int count = 0;
 	ext2_fsblk_t first_block = 0;

+	BUG_ON(maxblocks == 0);
+
 	depth = ext2_block_to_path(inode,iblock,offsets,&blocks_to_boundary);

 	if (depth == 0)
--- a/fs/ext2/xip.c
+++ b/fs/ext2/xip.c
@@ -37,6 +37,7 @@ __ext2_get_block(struct inode *inode, pg
 	int rc;

 	memset(&tmp, 0, sizeof(struct buffer_head));
+	tmp.b_size = 1 << inode->i_blkbits;
 	rc = ext2_get_block(inode, pgoff, &tmp, create);
 	*result = tmp.b_blocknr;

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